man: update man pages to say $HOME when accurate

Fixes #386.

man/man1/acid.1

@@ -84,7 +84,7 @@ obtains standard function definitions from the library file
 architecture-dependent functions from
 .BR \*9/acid/$objtype ,
 user-specified functions from
-.BR $home/lib/acid ,
+.BR $HOME/lib/acid ,
 and further functions from
 .B -l
 files.
@@ -499,7 +499,7 @@ acid: cont()
 .br
 .B \*9/acid/truss
 .br
-.B $home/lib/acid
+.B $HOME/lib/acid
 .SH SOURCE
 .B \*9/src/cmd/acid
 .SH "SEE ALSO"

man/man1/acme.1

@@ -300,7 +300,7 @@ Delete window without checking for dirtiness.
 Write the state of
 .I acme
 to the file name, if specified, or
-.B $home/acme.dump
+.B $HOME/acme.dump
 by default.
 .TP
 .B Edit
@@ -403,7 +403,7 @@ commands named as arguments.
 Restore the state of
 .I acme
 from a file (default
-.BR $home/acme.dump )
+.BR $HOME/acme.dump )
 created by the
 .B Dump
 command.
@@ -745,9 +745,9 @@ and
 .I awd
 reside.
 .SH FILES
-.TF $home/acme.dump
+.TF $HOME/acme.dump
 .TP
-.B $home/acme.dump
+.B $HOME/acme.dump
 default file for
 .B Dump
 and

man/man1/rc.1

@@ -806,6 +806,10 @@ is set to its process id.
 .B $home
 The default directory for
 .BR cd .
+Defaults to
+.B $HOME
+or else
+.LR / .
 .TP
 .B $ifs
 The input field separators used in backquote substitutions.

man/man1/sam.1

@@ -500,7 +500,7 @@ Plan 9 command.
 .BI \*acd " directory
 Change working directory.
 If no directory is specified,
-.B $home
+.B $HOME
 is used.
 .PD
 .PP